In today's semiconductor manufacturing industry, particles are defects that can destroy a semiconductor device by either affecting features at the level at which the particle occurs, or other features in other levels of the semiconductor device. Various lithography tools are used to form patterns in the various device layers of the semiconductor device. Particles in such lithography tools cause a defective pattern to be formed. Contaminating particles may include skin, bacteria, dust, silicon particles, metallic particles, and the like. The particles may emanate from the surface of the semiconductor wafer itself, or they may be generated by the manufacturing equipment used to process the wafers.
Semiconductor photolithography tools such as scanners and steppers include highly precisioned vacuum chucks to transport wafers throughout the system and to secure the wafer in the desired position when a pattern is being formed on the wafer. It is critical that the wafer surface includes a uniform height with respect to the exposure system, especially as technology progresses to producing nanometer-sized features in the patterns being projected onto the wafer surface in the photolithography tool. As such, the vacuum chucks used in the semiconductor manufacturing industry are manufactured to miniscule uniformity tolerances so that there is virtually no deformation of the wafer and the wafer surface being exposed is at a highly uniform level. Particle contamination that occurs on the exposure chucks of such lithography tools causes the wafer surface to deform, thereby deviating from the projected image plane and creating defocus spots or “hot spots” in the pattern formed on the wafer. These defocus spots distort the pattern formed on the wafer which can destroy device functionality. It is therefore imperative to maintain a pristine vacuum chuck in such lithography systems.
One way to remove particle contamination from a chuck is to mechanically open the lithography tool and physically wipe down and clean the chuck. This is obviously undesirable as it will expose sensitive components to conditions external to the highly controlled environment of the tool, and also possibly induce hardware related issues. Such disturbances carry the potential for extended downtime due to troubleshooting/repair of hardware, metrology setups, re-qualification and re-testing that must be carried out prior to releasing the system for manufacturing use. Moreover, by opening the system, further particle contamination may be introduced and various mechanical settings may be disrupted. It would therefore be desirable to clean the tool using a vehicle that is automatically and quickly cycled throughout the tool, precluding the need to open the tool. Upside-down (USD) wafers with highly-polished surfaces are known to attract particles that may be contained on a chuck, for example. A shortcoming of this approach is that many advanced photolithography tools include continuous vacuum clamping of the wafer to the chuck to avoid repositioning or other distortion of the wafer and pattern. Because the chucks and/or the vacuum rings that contact the polished semiconductor wafer surface are formed of highly-precisioned material such as ZeroDur® ceramics or other ceramics and plastics, the confronting surfaces are so smooth that a virtually perfect vacuum seal is formed between the wafer and the chuck or vacuum ring. Therefore, the technique of using USD wafers on continuously vacuum clamping chucks, is precluded because the vacuum seal prevents the release of the wafer from the vacuum chuck using the automated robotics used to transfer the wafer, i.e. to load and unload the wafer onto the chuck.
It would therefore be desirable to provide a method for cleaning a technologically advanced photolithography tool without having to open the system and by using USD wafers that can be cycled through the lithography tool using the automated robotics conventionally associated with such tools.